[Landscape Pattern Vulnerability and Its Driving Forces in Different Geomorphological Divisions in the Middle Yellow River].

The ecological environment of the middle Yellow River is highly vulnerable. Conducting a scientific assessment of landscape pattern vulnerability holds great significance, as it serves as the basis for the rational construction of the ecological environment in this area. Based on five periods of land use data from the middle Yellow River from 1990 to 2018, the landscape pattern vulnerability index was employed to analyze the spatio-temporal evolution of the landscape pattern vulnerability. Furthermore, the influencing factors for landscape pattern vulnerability in different natural geomorphological divisions were explored using an optimal parameters-based geographical detector model. The results showed that:① From 1990 to 2018, cultivated land (which accounted for 36.96 % to 39.97 % of the area) remained the predominant landscape in the middle Yellow River. Among all landscape types, cultivated land and construction land exhibited the most significant changes. The area of cultivated land decreased by 10 185.00 km2, whereas the area of construction land increased by 7 678.46 km2. ② From 1990 to 2018, the landscape pattern was dominated by low and medium vulnerability and accounted for 70 %-80 % of the total area. The high and higher vulnerability areas were concentrated in the loess hilly and gully region, whereas the lower vulnerability area was concentrated in the valley plain and the earth-rock mountain regions. During this period, landscape pattern vulnerability underwent an incipient decrease, followed by a subsequent increase. From 1990 to 2000 and from 2000 to 2005, the changes in the level of landscape pattern vulnerability were dominated by a "reduction in the degree of vulnerability". However, from 2005 to 2010 and from 2010 to 2018, it was mainly an "increase in the degree of vulnerability". ③ Annual precipitation and NDVI were the main factors influencing the vulnerability of landscape patterns, whereas the influencing factors varied across different natural geomorphological divisions:the loess hilly and gully region and the earth-rock mountain region were dominated by natural factors, with annual precipitation and DEM being the dominant factors, respectively; the loess plateau tableland-gully region, valley plain region, and sandy land and desert region were dominated by human factors, with population density, degree of land use, and distance from roads being the dominant factors, respectively. The interaction results of any two influencing factors were manifested as two-factor enhancement or nonlinear enhancement. Risk detection revealed that high vulnerability areas of landscape patterns in different natural geomorphological divisions were distributed over distinct ranges of their corresponding dominant factors. Therefore, in the practices of ecological management in the middle Yellow River, appropriate management strategies should be implemented based on the vulnerability characteristics of different natural landforms, to further improve the ecological management level of the watershed.

Evaluating soil-water conserving performance of land management strategies for spoil tips on the Chinese Loess Plateau.

Surface runoff decrease (SRD) and sediment concentration change (SCC) are accountable for sediment reduction by anti-erosion strategies. Using a design of horizontal stages, contour trenches, fish-scale pits, as well as their combinations, this study evaluated the two components for sediment reduction after the implementation of various land management strategies on steep spoil tips. The study highlighted the interactions between SRD and SCC in reducing sediment, and characterized the temporal variations of sediment-reducing capacity by SRD and SCC. Results showed that slope erosion was well controlled with control ratios of sediment yield ranging from 0.4 to 0.59, 0.2 to 0.22, for horizontal stage- and contour trench-based strategies, respectively. Sediment-reducing benefit by SRD accounted for 52%-77% of the total sediment reduction and highly determined the performance of SCC. Quadratic relationships between sediment-reducing capacity by SCC and that by SRD were observed. The function of SCC only operated when the sediment-reducing capacity by SRD reached a certain threshold. These thresholds varied greatly in the range of 0.75 kg m-3-0.91 kg m-3 and 0.61 kg m-3-0.66 kg m-3 for horizontal stage- and contour trench-based strategies, respectively. The upper limits for sediment-reducing capacity by SCC varied in the range of 0.32 kg m-3-0.44 kg m-3 and 0.63 kg m-3-0.76 kg m-3 for horizontal stage- and contour trench-based strategies, respectively. An efficiency coefficient of 55% and an M-N ratio of 1:1 indicated that sediment-reducing benefits by SRD and SCC were effectively exerted by combining contour trenches and fish-scale pits. The findings emphasized that the application of land management strategies must be considered based on particular goals to restore spoil tips. In practice, if targeted to enhancing sediment-reducing efficiency, contour trenches and fish-scale pits should be primarily considered. However, if the aim is to decrease water consumed for sediment control, then horizontal stages should be principally considered.

2-phosphanylphenolate nickel catalysts for the polymerization of ethylene.

The previously unknown methallylnickel 2-diorganophosphanylphenolates (R=Ph, cHex) were synthesized and found to catalyze the polymerization of ethylene. To explore the potential for ligand-tuning, a variety of P-alkyl- and P-phenyl-2-phosphanylphenols was synthesized and allowed to react with [Ni(cod)(2)] (cod=1,5-cyclooctadiene) or with NiBr(2).DME and NaH. The complexes formed in situ with [Ni(cod)(2)] are generally active as ethylene polymerization catalysts with all the ligands tested, whereas the latter systems are inactive when 2-dialkylphosphanylphenols are applied. M(w) values, ranging from about 1000 to about 100000 g mol(-1), increase for various R(2)P groups in the order R=Ph